The present invention relates to measuring, in a reference frame, angular displacements of a spin axis of a carrier moving along a trajectory. The angles of inclination are generally angles referred to as "yaw" and "pitch".
There are already numerous apparatuses in existence for measuring the inclination of a privileged axis tied to a carrier. Use can be made in particular of spinning mass gyros mounted on gymbals provided with angle sensors. The rotary contacts and the bearings of such apparatus reduce their reliability. Measurement errors are cumulative over time. Strap down systems are also known having three gyro measurement axes, using spinning mass, laser, or optical fiber rate gyros. Such solutions are expensive and often bulky.
A particularly important, although non-exclusive, application of the invention lies in the guidance system for a spinning projectile having a short flight time. It is then necessary at all times and to within a few degrees to know both the angle of inclination and the roll angle, even though the speed of rotation can be several revolutions per second. On such projectiles, it has been common practice to use free gyros having spinning masses driven by an electric motor or launched by a spring, by compressed gas, or by combustion gases. Such free gyros mounted on gymbols suffer from the drawbacks mentioned above. It is hardly possible to use a coupled-component inertial navigation system on such projectiles because the cost, mass, and volume of such systems are too great, and also because many such systems are sensitive to acceleration.